appendix b: statics and cohesion
by Phoenix Satori
Summary: the science of bubbles: or, the peril of tears in space.


this, too, can be read as entirely self-contained, but it -like 'appendix a'- also provides some important context and actual science!exposition referenced in chapter five of 'a feat equal' (still forthcoming). there's also a character mentioned at the beginning who features in 'this moronic episode,' but you don't *need* to've read either work to understand what's happening below. just enhances the overall experience if you have. ;)

 **appendix B: statics and cohesion**

( _see also: Kiyo Mizu_ )

[the cost vs benefit assessment: three years prior to the Quirk Registry Incident]

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Katsuki clearly remembers their first, post-Hari* training session: Uraraka, crumpled against the wall in a spent, boneless heap, sluggishly twisting the lid off her Ryukyu-skinned tumbler, and dropping the tips of her sweaty fingers through the opening like that's a normal fucking thing for a human adult to be doing. Next thing he knows, the tumbler's clattering to the floor, empty, and Uraraka's guiding a gently wobbling but otherwise perfectly round liquid orb to her lips to suction off a surface layer.

She catches him looking and lets her fingers fall away, leaving the rippling bead in a fixed hover near her face. The light refracted in the bubble has a prismatic effect on the matte color of her eyes that distracts him momentarily from the weird wonder of the bubble itself.

Perking up somewhat, "Pretty neat, right?" She glows with weary pride, which for some reason makes him feel _hunted_.

Instead of answering directly, "The fuck am I looking at?" Katsuki snaps, partially in a defensive bid for his upset equilibrium. She smiles a mile wide.

"Science!" His face twists with scorn at this over-broad non-answer, which makes her _giggle_. Somehow, he senses uneasily, this is related to the forever short fuse of his temper, mysteriously refusing to light. "This's how water behaves in zero G," she explains, pointlessly, because fucking _duh_ , "This's how most liquid behaves in zero G, actually," Uraraka continues, closing one eye and gauging the distance between them like she's lining up a clean shot –because that's precisely what she's doing. She blows a measured breath at the fist-sized sphere to send it flying toward him. It oscillates like crazy as it travels, but the overall integrity of its shape is never truly compromised. Like a carefully cast curling stone, the bubble coasts to a leisurely stop just within arm's reach. "Denser stuff wobbles less, but it all mostly balls up. That's the _real_ reason you're not supposed ta' cry in space –not 'cause no one can hear you, but 'cause your tears'll bubble up n' stick to your eyeballs and _blind_ ya'." He files this information away, along with the less conspicuously useful observation that Uraraka falls back pretty hard on _Kansai-ben_ ** when she's fatigued.

Experimentally, Katsuki sinks his finger into the sphere, tapping at a couple of smaller bubbles forming within to see if it's possible to dislodge them. One bead gets swept up and around the circumference of the larger bubble, but can't quite spin itself free, while the other flubbers right the fuck out of there. He intercepts the bubble on its wonky-ass flight path with the same finger he used to scoop it out, and flicks the thing into his mouth like a piece of popcorn. General strangeness aside, swallowing turns out not to be the existentially challenging experience he expects.

Across the room, another peal of soft, tired laughter. Uraraka's got her head tilted back against the wall, watching him with a kind of listless delight.

"Wanna guess what makes the magic happen?"

"Increased surface tension." He responds readily, having had plenty of time to work through his basic understanding of statics and cohesion and arrive at the only logical conclusion. Uraraka spreads her fingers where they're resting against her thigh, near the lower hem of her shorts, performing an utterly underwhelming banzai of congratulations.

Candidly, "So smart, Bakugou-kun."

"Better fucking believe it," he snorts, haughty.

Katsuki very deliberately looks away from sleepy fucking Sunshine to consider her bubble again instead, and what it could mean if they put in the effort to develop their tentative whatever-the-hell-this-is into something proved, and substantial. This sets him spinning out across a landscape of a thousand, a million, a _lifetime_ of possibilities, all predicated on _someone else's_ quirk. Internal alarms blare at Mic-pitch and he feels himself breaking out in a cold sweat as the foundation of everything he is threatens to give way.

"Bakugou-kun…?" Comes the sudden, wary hail from across the room.

Annoyed that she won't leave him to wig the shit out in fucking peace, "Can it, Moonface, I'm thinking." She sputters at his off-the-cuff epithet, but recovers fast and defies him immediately.

"What'cha thinkin' about?"

"Whether or not the shit-wrecking potential of partnering up is worth having to listen to all your shitty, distracting questions." Katsuki snarls. Unsurprisingly at this point, Uraraka has the wrong fucking reaction, and beams at him. Reckless joy blooms bright in her expression, and what the actual _shit_ , did his heart just _skip a fucking beat_?

"You wanna partner up?" There's a… _weepy_ quality to her voice he doesn't understand until, "With _me_?"

Unfortunately for Uraraka, he doesn't answer stupid questions, so he straight up ignores her, lapsing into angry silence. Then, remembering his long-since abandoned task of packing up, he gives her his back to continue where he left off.

When he finishes, he drags his workout bag up over his shoulder and stands, coming up right beside the bubble he will come to gradually regard as emblematic of forces beyond his control –like, for example, Uraraka and her physics-breaking fucking quirk—and unceremoniously chomping it out of the air without a second thought. Next he advances on Uraraka, who looks dazed as she packs away the last of her own belongings and zips her bag closed.

Heedless of his approach, she startles when he holds his hand down to her. Even after the initial shock wears off, though, she continues to stare at his hand like accepting it means tacitly agreeing to let him pull her up and put her through the wringer all over again. It isn't 'til he impatiently starts to withdraw that she finally snaps out a hand to grab him.

"Same time, next Saturday." He says, and it's not a question. And then there's that relentless fucking smile again, like her dumbass misgivings've passed, and like she might also be eager to see how far they can push this. Except this time their hands are linked and he's tugging her to her feet and she's abruptly too fucking _close_ and he can still fucking _taste her_ —

"You're on," Uraraka accedes, fire in her eyes.

Katsuki gulps back the phantom sweetness, and resigns himself to this already-unfurling hell of his own making.

* * *

*hari, as in 'hari senbon': 'needle' quirk. see 'sitting in a tree' for details.

**Kansai-ben: uraraka's hometown dialect, which i *adoooooore.*

***'banzai of congratulations' is probably (read: definitely) redundant, but i try very hard not to think about it.

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i swear to marangoni i'm still working on chapter five of a feat equal. and! i'm about halfway done, so it shouldn't be too much longer before that surfaces. keep your eyes peeled, loves~


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